1. Field of the Invention
The present invention relates to a catalyst composition for transalkylation of alkylaromatic hydrocarbons and to a process for production of xylene. More particularly, the present invention relates to a catalyst composition for production of xylene from a feedstock containing C9 alkylaromatic hydrocarbons by transalkylation and to a process for production of xylene.
2. Description of the Prior Art
Transalkylation of alkylaromatic hydrocarbons is one of the industrially important reactions which is applied to the production of benzene and xylene from toluene by disproportionation and the production of xylene from toluene and methylbenzene by transalkylation. There have been proposed a number of catalyst systems for this reaction. Among them is crystalline aluminosilicate zeolite (such as faujasite and mordenite) which is known as an effective catalyst. Mordenite is particularly active in transalkylation of alkylaromatic hydrocarbons.
Unfortunately, mordenite used alone is not satisfactory in activity and catalyst life; therefore, it is used in combination with a metal from Group VIB (such as chromium, molybdenum, and tungsten) or a metal from Group VIII (such as iron, cobalt, nickel, and platinum metal), as disclosed in U.S. Pat. No. 3,729,521. In addition, there is disclosed a catalyst which substantially consists only of mordenite and rhenium, in Japanese Patent Publication No. 45849/1987. These catalysts, however, are not wholly effective for transalkylation in production of xylene from C9 alkylaromatic hydrocarbons (including ethyltoluene). Incidentally, J. Das et al. reported transalkylation of feedstocks containing C9 alkylaromatic hydrocarbons by xcex2-zeolite (Catalysis Letters, vol. 23 (1994), p. 161-168). In actuality, this process is not satisfactory in xylene yields. Practically, there exists no efficient way of producing xylene from C9 alkylaromatic hydrocarbons containing ethyltoluene.
It is an object of the present invention to provide a catalyst composition for efficient production of xylene from a feedstock containing C9 alkylaromatic hydrocarbons by dealkylation and transalkylation. It is another object of the present invention to provide a process for producing xylene.
C9 alkylaromatic hydrocarbons are of low industrial value and are usually consumed as fuel. The present inventors paid attention to ethyltoluene and trimethylbenzene contained in C9 alkylaromatic hydrocarbons, because ethyltoluene can be converted into toluene by dealkylation and two moles of toluene or toluene and trimethylbenzene can be converted into xylene (which is industrially useful) by transalkylation. There has been no way of efficient dealkylation of ethyltoluene into toluene, which leads to low yields of xylene. The catalyst composition of the present invention is capable of efficient dealkylation of ethyltoluene into toluene and efficient production of xylene by transalkylation.